Electric circuit breakers of the air or gas-blast type



May 6, 1958 A. ROXBURGH' ET AL ELECTRIC CIRCUIT BREAKERS OF THE AIR- OR GAS-BLAST TYPE Filed Feb. 21, 1956 3 Sheets-Sheet l maazwr H y 1953 A. ROXBURGH ETAL 2,833,896

ELECTRIC CIRCUIT BREAKERS OF THE AIR- OR GAS-BLAST TYPE Filefi Feb. 21. 1956 5 Sheets-Sheet 2 1- FIG .2.

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ELECTRIC CIRCUIT BREAKERS OF THE AIR- OR GAS-BLAST TYPE Filed Feb. 21, 1956 3 Sheets-Sheet 3 HVVENTORJ QLBERT' ROX BUPGH HLBERT L H 3 M f m 1 MM ELIEIC'IRIC .CIRCUIT BREAKERS .OFTHE AIR-"OR GAS-BLAST TYPE Albert .Roxhurgh, Willesden, London, and Albert Leigh, Kenton, Harrow, England, assignors to The British Thomson-Houston Company Limited, London, England, afBritish company Application February 21,1956,Serial N 0. 566,973

Claimspriority, applicationGreat Britain February .23, 1915.5

:18 Claims. '(Cl. 200 -148) This invention relates to electric circuitinterrupters of the airor gas-blast type, and particularly to such circuit interrupters of the kind wherein aresistor is connected in parallel with the circuit interrupting contact gap or gaps "for controlling the recovery voltage rise or otherwise improving the circuit interrupting characteristics of the interrupter.

Circuit interrupters of this kind are known in 'Which a gap is included in series with the resistor, the electrodes of said gap and the resistor being thus connected in parallel'with the main or circuit interrupting contacts, so that under certain conditions of recovery volt-age rise the gap will break down and permit passage of current through said resistor.

-In a common arrangement of circuit interrupter of the "kind above referred to, the main or circuit interrupting contacts are mounted within .a contact chamber and biased to the closed position, being opened by the application of air pressure to said contact chamber; the invention is eminently although not exclusively, applicable in such circuit interrupters.

According to the presentinvention inan air or gas blast electric circuit interrupter having a resistance connected by means of a series gap in parallel with the circuit interrupting contact gap or gaps, a space within which the electrodes of said series gap are positioned is provided with pressure reducing means responsive to flow of air or gas produced during opening of the said circuit interrupting gap or gaps, whereby to facilitate breakdown of said series gap. Conveniently said space may, for'the purpose above set forth, be arranged so as tobe subject 'to reduction of pressure due to flow of the gas including the use of air, from a main contact chamber. In addition, the electrodes may be positioned within an auxiliary chamber communicating with a main contact chamber at or located adjacent to a discharge port or ports in said main chamber.

According to a further feature of the invention, with a view to obtaining a greater reduction in pressure at the above referred to series gap, the space within which the electrodes are positioned is connected with ejector means through which air or gas is caused to flow on opening of the circuit breaker and to entrain air or gas from said space and thereby reduce the pressure within said space substantially below atmospheric pressure.

The ejector means may be supplied with pressure air or gas from a ch-arnber enclosing the main contacts directly from the upstream side of the main contacts or may be arranged within a discharge passage on the downstream side of the main contacts.

In practising the invention, it the gap is able to extinguish the resistor current upon return of the pressure conditions at the gap to normal, then the circuit interrupter may or may not include isolating contacts as part of the interrupter itself, since there will be no residual current to be interrupted after the electrode gap has extinzuished the resistor current, and therefore the open United States Patent "ice .2 circuit conditions are maintained for so long astthe main contacts are open. In cases in which isolating contacts are provided as part of thecircuit interrupter-itself, means may or may not be provided whereby after opening of the isolating contacts the air or gas pressure will be released from the contact chamber and the auxiliary chamber. and reclosure of the main contacts thereby effected. The opening of the isolating contacts may, forexample, ibe efiected by the usual means so as to occur afterextinction of the current in the resistor.

in application for United States Serial $10,489,564, now Patent No. 2,794,886, issued June 4, .1957, circuit breakers of the kind referred to are claimed wherein a resistorand seriesgap areprovided ashereinbef-ore indi- .cated, and wherein said gap is arranged to break down and permit passage of current through saidresistor when the main contacts are opened, and means 'are provided for the application of air or gas pressure to said series gap whereby .to quench the 'arc in the latter and terminate :the flow of current through the series resistor. in carryingrout the invention of said application, meansJma-y be provided for applying the .air or gas pressure :to the series gap with a time delay after opening of the .main contacts.

Incarrying out the present invention, the arrangement is preferably such that after the main contacts have been opened .to extinguish the current, pressure air or gas will be supplied to the space ,in which the electrodes .are 1308i .tioned, whereby to increase the breakdown voltage of the latter and sofaci-litate interruption of the resistor current, this .feature of the present arrangements being thus ,in accordance with the invention described and claimed in application for United States Serial .No. 489,564, new Patent'No. 2,794,886, aforesaid.

Reference will now bernade by way ofuexample to :the accompanying drawings, in which:

Fig. .1 is a sectional elevation showing one embodiment of the invention,

.Fig. 2 is an outline elevation with reference to which one illustration of the arrangement of Fig. 1 .in'combination with an isolating switch means will be described,

Fig. 3 is an outline elevation showing part of a .circuit breaker comprising a duplication of .the contact arrange ment employed in Fig. 2, and

Figs. 4 and 5 are sectional elevations showing, respectively, two .further embodiments of the invention.

In Fig. 1 the circuit breaker includes a main contact chamber which is of the-otherwise well known type comprising a horizontal tubular insulating member 1 extending from a conductive assembly 2 mounted on a tubular supporting insulator 3, the lower end of which is secured to a member 4 which in turn is suitably mounted on a main framework or base .(not shown) for the circuit breaker. The tubular member 1 carries at its free end a contact and line terminal unit or assembly 5.. The assembly 5 comprises a metal casing 6 having an end wall 7 which closes the adjacent end of the tube 1, the assembly 5 being secured to the member 1 such as by a metal ring 8 of the usual construction secured .to the wall 7. The other end of the member 1 is secured to the metal assembly 2 by means of a similar ring 9.

The Wall 7 is formed with a cylinder 10 which extends inwardly and coaxially of the insulating member 1, and a tubular moving contact member 11 extends through an aperture at 12 in the wall 7. Contact 11 includes a flange 13 which forms a piston working within the cylinder 10 and operable by air pressure in said cylinder. The contact 11 is adapted .to engage at its .inner :end with a fixed rod 14 which extends from the conductiveassembly 2, being mounted therein by means of a metal tube 15 which is secured, such as by welding, to an end-plate 16'closingthe assembly 2;

The various parts of the circuit breaker are shown in Fig. 1 at a stage during the interruption of the current as will hereinafter be described.

The metal casing 6 is formed as a cylinder in which is movable a piston 17, this piston being biased by means of a compression spring 18 into engagement with the adjacent end of the tubular moving contact 11 so as in the normal condition of the switch parts to hold the latter in contact with the end of the fixed contact 14. The piston '17 is provided with vents such as 19 whereby free movement of said piston is permitted, said vents equalising the pressure on the two sides of the piston whereby the latter will not be responsive to the pressure conditions within the casing 6.

The space within the cylinder 12 in rear of the piston 13 is vented to atmosphere by a passage Zti.

The casing 6 includes a further cylindrical portion 21 provided with a plurality of outlet ports such as 22. The internal diameter of said cylindrical portion 21 is less than that of the main space within the contact unit and the total area of the discharge passages 22 is greater than the cross-sectional area within the portion 21, so that the latter constitutes a throat through which the air will be discharged from the contact unit through said openings to atmosphere. This throat may be given a venturi form as shown at 21a.

The resistor in this embodiment of the invention comprises a resistance element 28 housed within a tubular insulating casing 2? conveniently supported as shown with its axis parallel with that of the member 1. The casing 29 is mounted by means of a conducting member'3t) which serves to connect one end of the resistor with the assembly 2 and thereby with the fixed contact 14, and by means of a conductive member 31 secured to the casing 6. The member 31 constitutes a fixed electrode, the upper end of said member extending horizontally into the casing 29 through the end of the latter and co-operating with a fixed electrode 32 which is mounted on and extends through a partition 33 in the casing being connected with the adjacent end of the resistor 28. The partition 33 defines an auxiliary chamber 34 of comparatively small volume at the left hand end of the casing 29. This chamber is connected by means of a pipe 35 with a port 21b at the throat of the casing portion 22 so that pressure conditions within the throat will be transmitted to the auxiliary chamber 34 and thereby to the gap between the electrodes 31 and 32.

The space within the tubular insulating casing 1 and a corresponding space within the assembly 2 is in communication, by way of the tubular insulator 3, with a control valve 37 arranged within the member 4. This control valve is normally biased on to its seat 38 by means of a compression spring 39. The space below the valve is connected by a pipe 40 with a source (not shown) of compressed air or gas. 41 extending in airtight manner through the end cover 42 of the member 4, which stem is connected with suitable operating mechanism adapted to open said valve when the circuit breaker is to be opened such as in response to tripping mechanism for said circuit breaker. Since such operating mechanism for the valve is well known in the art, further description thereof is deemed unnecessary herein.

The contact unit is provided with a terminal member 43 adapted to be connected with one supply line and a second terminal member 44 is carried 'by the member 16 for connection with the other supply line. As hereinbefore indicated, circuit-breakers of the kind described are usually employed in conjunction with an isolator switch such as in the manner shown in Fig. 2, wherein the terminal 44 constitutes a fixed contact adapted to be engaged by an isolator blade 45 which is movable into and out of engagement with the contact 44. In the example shown in Fig. 2 the blade 45 is fixedly mounted on the upper end of an insulating pillar 46 mounted for ro- The valve 37 includes a stern tation about its vertical axis on a member 47', the blade having electrical contact with a terminal member 44' adapted to be connected with the second mentioned supply line and having a pivotal connection at 45 with the blade 45 so as to permit the rotational movement of the latter, whilst the terminal member 44, remains fixed in space. Member 47' together with the member 4 are mounted for example on a fixed framework 48. The general arrangement of circuit-breaker shown in Fig. 2 is in itself well known to those skilled in the art, and it is therefore deemed unnecessary herein to describe the operating mechanism in detail. It is sufficient to state that an air operated servomotor or other means are provided for rotating the insulating pillar 46, the control means for this servomotor or means being suitably combined with that for the control valve 41 so that after the latter has been opened the isolator 45 will be moved out of engagement with the contact 44 so that the contacts within the member 1 may then be reclosed by closure of the control valve 37.

It will be understood that the arrangements of Fig. l and of Figs. 4 and 5 are, however, not limited to the general arrangement of circuit breaker described with refererence toFig. 2, but has general application.

in the operation of the arrangement shown in Fig. 1, during the normal closed condition of the contacts 11 and is, me control valve 3'? is cicsed so that the spring 18 urges the contact 11 into engagement withthe contact 14. is opened so as to apply air pressure to the spacewithg in the member 1. tact ll away from the contact 14. The pressure air-will then how across the gap between the contacts into the contact 11 and flows from the latter into the casing 6 by way of ports such as 11a in the moving contact, and is discharged to atmosphere by way of the ports 22. The ilow of air thus extinguishes the are drawn between the contacts in the usual manner. Under normal conditions of recovery voltage the gap be. $36211 the electrodes 31 and 32 will break down so that the resistor becomes connected effectively in parallel with the open main contacts i1 and 14-. The flow of air through the throat 21a results in a drop in static pressure therein due to the increased velocity of the air at the throat, and this drop in pressure is communicated by pipe 35 to the auxiliary chamber 34 to facilitate the break down of the gap, or the arrangement may be such that the gap would not normally break down at atmospheric pressure. The spacing between the electrodes may be such in relation to atmospheric pressure that at the normal line voltage the arc will not be maintained between said electrodes when the pressure in the auxiliary chamber 34 returns to normal, so that the current in the resistor 28 also is terminated. Circuit interruption may be thus completed or may be finally effected in the usual way by opening of the series isolator. Means responsive to the opening ol the isolator may be arranged also to close the main air or gas control valve 37.

The arrangement above described is applicable in circuit breakers according to appiication for United States Serial No. 489,564, now Patent No. 2,794,886, aforesaid.

in one embodiment of said circuit breaker as described in said application the arrangement is generally similar to that hereinbefore described by way of example, but the lateral cylindrical part of the contact unit houses a piston which is biased by a compression spring toward the main space within the contact unit so as normally to obstruct said ports. This cylinder is closed at its outer end, and said end is connected by means of a conduit with the space on the upstream side of the moving contact. Arrangements of this kind are included in the embodiments of the invention illustrated in Figs. 4 and 5.

Fig. 3 illustrates a circuit-breaker arrangement wherein two contact units 5A and 5B are mounted respectively on tubular insulating members 1A and 1B extending-op In order to open the circuit the controlj-valve 37- This air pressure will urge the conpositely from a common conductive assembly 2 and supported therefrom on a commonvertical insulating member 3. Resistors are provided at 28A and 28B in parallel with the contacts in the two units 5A and 5B respectively, theelectrodes 31A and 32A extending into the two auxiliary chambers respectively and the latter being connected respectively with the associated casings of the units 5A and 513 by means of pipes 35A and 35B. In this arrangement the assembly 2 is modified by the omission of the end cover 16, the contact 14 of Fig. 1 being duplicated within the tubular member 1B and the two fixed contacts being suitably supported such as by a spider member within the assembly 2.

Line terminals 43 and 44 are-mounted respectively on the two units 5A and 58, being for example connected with the line conductors directly or by means of a separate isolator switch or switches, or one terminal constituting a fixed contact of an isolator'switch such as in the arrangement of Fig. 2.

The circuit breakers illustrated in Figs. 4 and 5 are generally of the form hereinbefore described with reference to Fig. l, the same reference numbers denoting like parts on the same figures but includes provision in accordance with U. S. application Serial No. 489,564, now Patent No. 2,7 94,886, as will hereinafter be indicated. In Figs. 4 and 5 the assembly 2 is also mounted on a tubular supporting insulator such as 3 of Fig. l, but not shown in Figs. 4 and 5, which insulator is secured to a member which in turn is suitably mounted such as on a main frame-work or base of the circuit and includes a normally closed control valve (37, Fig. 1) which is opened in order to place the space within the member in communication with a reservoir or other source of pressure air when it is required to open the circuit breaker.

The various parts of the circuit breaker are shown in Figs. 4 and 5 at an intermediate stage during the interruption of the current as will hereinafter be described.

In Fig. 4 the chamber 34 is connected by means of a short pipe 1% with the inlet port 101 of a vacuum ejector comprising a casing M32 having mounted therein a venturi 103, with which is connected an air supply conduit 104 extending from a passage 105 in the casing 6 on the upstream side of the main contacts and thereby communicating with the pressure air within the member 1.

*In the embodiment of the present invention shown in Fig. 4, the discharge port 196 of the ejector is connected by means of a conduit 3.87 extending to a further cylindrical portion 21 of the assembly 5. The portion 21 forms a discharge passage from the main contacts and is provided with a plurality of outlet ports, such as 22, which ports are however normally closed, in accordance with U. S. application Serial No. 489,564, new Patent No. 2,794,886,, aforesaid, by means of a piston 23 which is movable in the cylinder 21 and is biased upwardly by means of a compression spring 24. The upward movement of the piston 23 is limited by a shoulder at 25 to a-position wherein said piston closes the ports 22. The outer end of the cylinder 21 is connected by a pipe 26 with a port '27 in the cylinder 10, the arrangement being such that whereas in the illustrated open position of the contact ll the piston 13 is to the left-hand of said port, in the normal circuit-closed position of said contact 11 the port 27 will be closed by the piston 13 against how of air from the-member 1 into the pipe 26. As in the Fig. 1 construction, the space in the cylinder in the rear of piston 13 is vented to the atmosphere by a passage 20.

For a purpose which will hereinafter appear the conduitlltlfl provided according to the present invention, is formed with a down-turned end 108 within the portion '21.

The contact'unit 5 is adapted to be connected with one supply line and the member 16 with the other supply line. As hereinbefore indicated, circuit-breakers of the kind described are usually employed in conjunction with an isolator switch and may be arranged in the manner fully hereinbefore described with reference to Figs. 2

and 3.

In the operation of the arrangement shown in Fig. 4, during the normal closed condition of the contacts 11 and 14 the control valve 37 (Fig. 1) is closed so that the spring 18 in Fig. 4 urges the contact 11 into engagement with the-contact l4 and the piston '23 occupies its uppermost position under the influence of the spring '24. :In order to open the circuit the control valve 37 is opened so as to apply air pressure to the space within the member 1. This air pressure will urge the contact'll away from the contact 14. The pressure air will then how across the gap between the contacts into the contact 11 and flows from the latter into the casing 6 by way of ports such as 11a in the moving contact. This operation occurs as soon as the contact '11 leaves the contact 14,-s0 that air pressure builds up within the casing :6 and, the

spring 24, being of insuflicient strength to resist said pressure, the piston 23 is moved downwardly to its illustrated position thereby to allow escape of the'air fromthe casing 6 to atmosphere by way of the ports 22. The flow of air thus extinguishes the are drawn between the contacts. Under normal conditions of recovery voltage, the gap between the contacts 31 and 32 will break down so that the resistor becomes connected effectively in parallel with the open main contacts 11 and 14. The operation as so far described is similar to that of the circuit breaker described in'U. S. application Serial No. 489,564, new Patent No. 2,794,886, aforesaid. However, at the same time that the air or gas pressure acts on the mov- 'i-ng contact, pressure air or gas flows through the port and conduit 104 to the ejector and entrains air from the chamber 34 whereby to reduce the air pressure within said chamber substantially below atmospheric pressure and facilitate breakdown of the gap between electrodes 31 and 32. The pressure air and the entrained air is discharged from the ejector through the conduit 107 and the outlet ports 22.

As fully described in the complete specification of U. S. application Serial No. 489,564, now Patent No. 2,794,886, aforesaid to which attention is hereby directed,

the movement of the moving contact 11 to the illustrated fully open position results in the port 27 being uncovered by the piston 13, so that air pressure is applied through the pipe ,26 to the underside of'the piston 23. As a result, after a predetermined time interval, dependent on the operating air pressure within the member 1 and .on the dimensions of the pipe 26, the pressure below the piston 23 will build up to that above said piston and the latter will ,be returned to its original position so as to close the discharge ports 22, and thereby terminate the,

flow of air through conduit 1 07. The air pressure within the member 1 is thus applied also to the chamber 34 so as to increase the di-electric strength between the electrodes 31 and 32 and thereby facilitate interruption of the resistor current. Circuit interruption is thus completed.

:In order to reclose the circuit the valve 37 (see Fig. .1) is closed and an exhaust valve, the head of which is shown at 3% in Fig. 1, is opened to connect the contact chamber with .atmosphere.

If the circuit interrupter includes a series isolator as part thereof, such as in the arrangement of Fig. .-21for example, means responsive tothe opening of the isolator may be arranged also to open the exhaust :valve zwhereby to release the air or gas pressure maintained at'this stage within the contact unit. The main contacts 11 and 14 of Fig. 1 will then reclose.

It will be understood that automatic reclosing operation can be provided by the usual means which, however, in application to the arrangement above described will be arranged to release the air pressure from the contact unit, namely by opening suitable exhaust valve means, as well as by closing the main air or gas control valve.

In the embodiment illustrated in Fig. 5, the vacuum ejector is arranged directly within the discharge passage of the cylindrical part 21. The conduit 190 is extended from the chamber 34 to said cylindrical portion and communicates with the inlet port of a. tubular ejector body 110 which is secured within said cylinder 23 on the downstream side of the main contacts. This body is provided with an end member 111 of disc form completely closing the passage through the cylinder 21 except for a central orifice which is formed as a venturi 112. The body 11h is provided with an outlet venturi 115. The lower end of this outlet venturi is positioned so as to be engaged by the upper end of the piston 23 in the uppermost position of the latter.

In the operation of the arrangement according to Fig. 5, on opening of the circuit breaker the air flowing from the ports in the moving contact 11 is discharged through the venturis 112 and 113 so as to entrain air and thereby exhaust air from the auxiliary chamber 34 and again reduce the pressure therein below the atmospheric pressure.

In the arrangement illustrated in Fig. 5, the outlet venturi 113 is eventually closed when the piston 23 rises and the air under pressure within the chamber 6 then flows upwardly through the conduit 1% into the auxiliary chamber 34 so that the air pressure therein is increased and the resistor current interrupted.

It will be seen that in the arrangements according to Figs. 1, 4 and 5, on opening the circuit breaker, the air pressure at the resistor electrodes is initially reduced considerably below the atmospheric pressure so as to provide a'lower (ii-electric strength between the electrodes whereby the latter will breakdown rapidly following a current interruption by the main contacts, and subsequently the di-electric strength of said gap is increased by the application thereto of an air at a pressure above atmospheric to facilitate interruption of the resistor current. It will be understood that the effectiveness of the auxiliary gap in interrupting the resistor current is dependent upon the ratio of the minimum and maximum air pressures at which said gap is operated, and the invention enables a large increase in said ratio to be obtained. For example in one embodiment, said ratio is increased in the order of 3.4 times by means of the invention.

It is to be understood, however, that the arrangements of Figs. 4 and 5 may be employed also, according to the present invention, without the means for closing the discharge openings from the contact chamber and thereby increasing the air pressure in the chamber 34 after current interruption at the main contacts.

What we claim is:

1. A gas blast electric circuit interrupter having main circuit breaker contacts, a chamber around said main contacts, means for supplying gas under pressure to said chamber for opening said main contacts and for extinguishing the arc therebetween, a circuit in parallel with said main contacts comprising a resistance and a gap in series, and means responsive to flow of gas through the gap between said main contacts in open circuit position for reducing the pressure in said series gap whereby breakdown thereof is facilitated.

2. A gas blast electric circuit interrupter having main circuit breaker contacts, a chamber around said main contacts, means for supplying gas under pressure to said chamber for opening said main contacts and for extinguishing the arc therebetween, a circuit in parallel with said main contacts comprising a resistance and a gap in series, means comprising a discharge port in said main contact chamber providing for the flow of gas therefrom, and means responsive to flow of gas from said main contact chamber on application of gas pressure thereto by said gas supply means for reducing the pressure in said series gap whereby breakdown thereof is facilitated.

3. A gas blast electric circuit interrupter having main circuit breaker contacts, a chamber around said main contacts, means for operating said main contacts and for supplying gas under pressure to said main contact chamher, a circuit in parallel with said main contacts comprising a resistance and a gap in series, and means providing for the flow of gas from said main contact chamber and for reducing the pressure in said series gap wherebrcakdown of said series gap is facilitated.

4. A gas blast electric circuit interrupter having main circuit breaker contacts, a chamber around said main contacts, means for operating said main contacts and for suppiying gas under pressure to said main contact chamher, a circuit in parallel with said main contacts comprising a resistance and a gap in series, means comprising a discharge port providing for the flow of gas from said main contact chamber, and means responsive to fiow of gas from said main contact chamber for reducing the pressure in said series gap whereby breakdown of said series gap is facilitated.

5. A gas blast electric circuit interrupter as claimed in claim 4, in which said gas flow responsive means includes ejector means connected to said main contact chamber to provide for the flow of gas therethrough prior to discharge thereof through said port on opening of said main circuit breaker contacts and for entraining gas from said series gap thereby to reduce the pressure in said series gap substantially below atmospheric pressure.

6. A gas blast electric circuit interrupter as claimed in claim 4, in which said gas fiow responsive means includes an auxiliary chamber arranged around said series gap and in communication with said main contact chamber at a point adjacent to said discharge port of said main contact chamber.

7. A gas blast electric circuit interrupter as claimed in claim 6, in which a restricted throat is formed in said main contact chamber communicating with the discharge port therein, and said auxiliary chamber is connected in communication with said main contact chamber at said restricted throat.

8. A gas blast electric circuit interrupter having main circuit breaker contacts, a chamber around said main contacts, means for operating said main contacts and for supplying gas under pressure to said main contact chamber, a circuit in parallel with said main contacts comprising a resistance and a gap in series, means providing for the flow of gas from said main contact chamher through the gap between said main circuit breaker contacts in open circuit position, and ejector means connected to said main contact chamber for reducing the pressure in said series gap whereby breakdown of said seies gap is facilitated.

9. A gas blast electric circuit interrupter as claimed in claim 8, in which said ejector means are connected with said main contact chamber for the supply of pressure gas therefrom directly from the upstream side of said main contacts.

10. A gas blast electric circuit interrupter as claimed in claim 8, in which a gas discharge passage is provided for said main contact chamber on the downstream side of said main contacts and said ejector means are arranged in said gas discharge passage.

ll. A gas blast electric circuit interrupter as claimed in claim 9, in which valve means are provided in the path of gas flow from said ejector means.

12. A gas blast electric circuit interrupter as claimed in claim 10, in which valve means are provided in the path of gas flow from said ejector means.

13. A gas blast electric circuit interrupter as claimed in claim 12, in which said valve means comprise a gas discharge port in said main contact chamber and a piston member movable Within said main contact cham her and adapted to open and close said gas discharge port.

14. A gas blast electric circuit interrupter comprising in combination, main circuit interrupting contacts, a chamber around said main or ntacts, means for supplying gas under pressure to said main contact chamber, a resistor and a pair of fixed electrodes connected in series in a circuit in parallel with said main contacts, said electrodes being separated by a gap which breaks down and permits passage of current through the resistor on opening of said main contacts, a pressure retaining chamber surrounding both of said electrodes, and means providing for flow of gas from said main contact chamber operative on opening of said main circuit interrupting contacts for extinguishing the arc therebetween and decreasing the static pressure on said electrodes and the gap therebetween whereby breakdown of the gap is facilitated.

15. A gas blast electric circuit interrupter comprising in combination, main circuit interrupting contacts, a chamber around said main contacts, a resistor and a pair of fixed electrodes connected in series in a circuit in parallel with said main contacts, said electrodes being separated by a gap which breaks down and permits passage of current through said resistor on opening of said main contacts, a pressure retaining chamber having a gas inlet and outlet means and surrounding the gap ends of said electrodes, means for supplying gas under pressure to said main contact chamber, means providing for flow of gas from said main contact chamber operative on opening of said main circuit interrupting contacts for extinguishing the arc therebetween and decreasing the static pressure on said electrodes and the gap therebetween whereby breakdown of the gap is facilitated, and means providing for the flow of gas under pressure into said electrode chamber operative following a time delay after opening of said main circuit interrupting contacts for increasing the static pressure on said electrodes and the gap therebetween and quenching the arc in the latter by said increase of static pressure whereby the flow of current through said resistor is terminated.

16. A gas blast electric circuit interrupter as claimed in claim 15, in which said valve means comprise a gas discharge port in said main contact chamber and a piston member movable within said main contact chamber and adapted to open and close said gas discharge port.

17. A gas blast electric circuit interrupter as claimed in claim 1.5, in which valve means are provided operative after opening of said main circuit interrupting contacts for closing said electrode chamber gas outlet means.

18. A gas blast electric circuit interrupter as claimed in claim 17, in which said valve means comprise a gas discharge port in said main contact chamber and a piston member movable within said main contact chamber and adapted to open and close said gas discharge port.

References Cited in the file of this patent UNITED STATES PATENTS 2,391,826 Flurscheim Dec. 25, 1945 2,453,555 Thommen Nov. 9, 1948 2,581,822 Thommen et a1. Jan. 8, 1952 2,596,254 Latour May 13, 1952 2,665,351 Forwald Jan. 5, 1954 2,794,886 Roxburgh et al. June 14, 1957 

